Musnad Ahmad 27:554

Abu Mu'awiyah narrated to us, Ubaydullah narrated to us, from Nafi', from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The person in Ihram shall not wear the burnous (hooded cloak), nor the shirt, nor the turban, nor the trousers, nor the leather socks, unless he is compelled to, in which case he should cut them below the ankles. And he shall not wear a garment touched by wars (a yellow dye) or saffron, unless it has been washed."